1. Field of the Invention
This invention relates to the electric control of the feed pressure of a hydraulic receiver, particularly for the input clutch on the first gear of a motor vehicle automatic transmission.
2. Discussion of the Background
For control of this type of clutch, so-called electronic control engine idling clutch release systems are known, such as the one described in the French Patent publication FR 2600597 of applicant, which make it possible to eliminate, on a vehicle equipped with an automatic transmission, the spontaneous tendency to "creep" from a stop, when handling considerations make this tendency undesirable.
The main difficulty encountered in the development of such systems appears during restarting, when the driver again presses on the accelerator and opens, in an essentially variable way, the throttle valve for a gasoline engine or the device for metering the Diesel fuel for a Diesel engine. Actually, it is very difficult to find settings that give a satisfactory result from the point of view of starting comfort, both for a start with a thin stream of gas, and for a "foot to the floor" (i.e. accelerator pedal completely depressed) start. The shortcomings are reflected by a jerking motion upon acceleration, which is unacceptable considering the standards of comfort required of modern automatic transmissions.
These shortcomings are explained by the fact that the engine idling clutch release systems known to date are activated by the simultaneous monitoring of preestablished conditions, particularly the speed of the vehicle, the speed of the engine, the output speed of the converter and the angular position .alpha.c of the fuel metering element of the engine, in relation to its idling position particular, for the latter, the condition most often imposed is: .alpha.c-/.alpha.c at idle.
Actually, the angular .alpha.c does not take into account:
the advantage which exists in being able to perform maneuvers at idle, precisely by using the "creeping" phenomenon characteristic of automatic transmissions. Actually, to cause engine idling clutch release to cease, it in necessary that .alpha.c&gt;.alpha.c at idle, which results from pressing on the accelerator in a perceptible way; PA1 the inevitable response time for filling of the input clutch cylinder which, although held in a mating position, is not able to transmit without a certain delay, albeit a minimum delay, the full engine torque during fully depressed accelerator pedal start. By nature, the measurement of .alpha.c does not allow any anticipation of the arrival of the torque. Anticipation would make it possible to eliminate the response time of the input clutch.
It is known how to eliminate said drawbacks of the known "engine idling clutch release" systems (i.e. clutch release while the engine is idling), by substituting for the measurement of angular position .alpha.c, a so-called "foot pressed" switch, inserted on the accelerator control. The switches known to date to fulfill this function, such as the one described in the previously mentioned French patent publication FR 2600597 of the applicant, exhibit a complex mechanical structure, which makes it possible for them, of course, to meet the multiple functional requirements including fluidtightness, protection of contacts, minimal friction, etc.--but at the expense of sometimes insufficient reliability and high cost.